Artificial lighting and plant
transpiration generates heat and humidity that can produce poor growing
conditions. Ventilation equipment must be capable of removing this
excess heat and humidity.
Equipment
overview
Exhaust fan:
Generally speaking, the exhaust fan (Fig
8.1) should be capable of removing (i.e. exchanging) the volume of air
in the room within 5 minutes. Consult your fan manufacture or
growshop for the best fan size and type. You will need to account for room
size; configuration of ducting (diameter, length and junctions/ bends);
inlet/ outlet filters; the maximum temperature of incoming air; and the
total wattage of all electrical devices in the growroom.
To
prevent condensate from pooling in the fan, mount the fan vertically in
ceiling as opposed to high on a wall.
Inlet fan:
Pushing air into the room (Fig
8.1) helps maximize the effectiveness and lifespan of the exhaust fan.
To ensure the exhaust fan is not restricted, use an inlet fan of
equivalent airflow capacity.
Tips for best airflow:
1. Where air is being moved through ducting,
centrifugal/ radial (or ‘mixed inline’) fans are the most efficient (Fig
8.2).
2. Where air ‘enters’ the fan unit/ ducting,
ensure it is mounted flush with a solid/ sealed surface of diameter at
least double the diameter of the inlet itself (Fig
8.1). A flange may be needed to achieve this.
3. Keep objects at least 1 meter (3 ft) away
from the inlet.
4. Position a diffuser screen on the opening.
A filter (preferably activated carbon) will help act as a barrier to
spores and pests.
Ducting:
For maximum fan efficiency keep ducting as short and straight as possible.
Where junctions are needed employ ‘Y’ junctions instead of ‘T’s. If
the diameter of ducting needs to change en-route, ensure this change is
gradual (~10 degrees).
Oscillating fan:
Usually operates 24 hours a day to ensure
air is always distributed evenly (but gently) throughout the room (Fig
8.1). This eliminates ‘hot spots’ i.e. zones prone to CO2
depletion or excessive humidity and temperature that are most likely to
occur nearest lights and dense foliage.
Relative location of inlet, exhaust and oscillating fans:
As a general rule, try to keep the air moving in one direction (this
creates and maintains air momentum).
The ideal configuration depends on many factors including room size and
shape, and the relative placement of equipment/ plants within the room.
As a general rule, locate the ‘inlet’ and ‘exhaust’ at opposite ends of
the room, with an oscillating fan maintaining the airflow direction
provided by the inlet (Fig
8.1).
For wider rooms especially, employ multiple inlets and exhausts and space
them evenly across the room’s width. This will help ensure all air
is replaced. To verify the system is working throughout the room,
routinely check temperature and humidity at various points.
Thermometers and hygrometers:
These devices provide minimum/
maximum data and will inform of the worst case scenario (Fig
8.1). Position the probe in that place of highest temperature/
humidity (i.e. typically directly beneath the lights and amongst the
foliage). However, for accuracy, shield the probe (or sensor) from
direct heat and light.
Growroom dimensions:
The more plants there are in a given
area, the quicker temperature and humidity will rise to extremes.
Therefore aim to minimise the number of plants. If this is not feasible
then ventilation rates must be increased.
Also, where over-heating is a problem, a
higher roof helps because the maximum temperature is further from the
plants (i.e. hot air rises).
For details on how to switch fans on and
off click here
